Aerosol deposition may supply a high diversity of airborne microbes, which can affect surface microbial composition and biological production. This study reports a diverse microbial community ...associated with dust and other aerosol particles, which differed significantly according to their geographical air mass origin. Microcosm bioassay experiments, in which aerosols were added to sterile (0.2 µm filtered and autoclaved) SE Mediterranean Sea (SEMS) water, were performed to assess the potential impact of airborne bacteria on bacterial abundance, production, and N2 fixation. Significant increase was observed in all parameters within a few hours, and calculations suggest that airborne microbes can account for one third in bacterial abundance and 50–100% in bacterial production and N2‐fixation rates following dust/aerosol amendments in the surface SEMS. We show that dust/aerosol deposition can be a potential source of a wide array of microorganisms, which may impact microbial composition and food web dynamics in oligotrophic marine systems such as the SEMS.
Key Points
Airborne bacteria are viable upon deposition in the ocean
Airborne bacteria contribute to bacterial production in surface seawater
Airborne bacteria contribute to N2 fixation in surface seawater
Extensive oceanographic data sets were combined with microbiological parameters to elucidate the tight coupling between glacial meltwater and heterotrophic bacterial production (BP) on the Getz Ice ...Shelf (GtzIS) in the Amundsen Sea. BP in the eastern GtzIS (EG; 85.8 pM Leu. h−1), where basal glacier meltwater upwells, was significantly higher than BP measured in the western GtzIS (WG; 50.6 pM Leu. h−1) and the Amundsen Sea Polynya (ASP; 27.8 pM Leu. h−1). BP in the EG accounted for 49% of primary production, which was greater than that of the WG (10%) and ASP (9.2%). Enhanced BP in the eastern GtzIS was not coupled with phytoplankton biomass, but correlated significantly with the freshwater fraction containing meltwater‐derived dissolved organic carbon (MW‐DOC). These results suggest that warming‐induced glacier melting weakens carbon sequestration efficiency in Antarctic coastal waters by stimulating heterotrophic metabolism that converts MW‐DOC to CO2.
Plain Language Summary
The Getz Ice Shelf (GtzIS) in the Amundsen Sea, the third‐largest ice shelf (34,018 km2) on the West Antarctic Ice Sheet, is regarded as a hot spot for producing large amount of glacier meltwater (144.9 ± 14 Gt yr−1). In general, the amount of dissolved organic carbon (DOC) from terrestrial sources is negligible in Antarctic waters, making DOC supplied by phytoplankton a major carbon source for heterotrophic bacteria growth. Although Antarctica's glacial ice shelves are presumably a large reservoir of organic carbon (ca. 5.5 Pg C), little is known about the effect of glacial melting on the supply of DOC available to heterotrophic bacteria. On the eastern GtzIS, where glacial meltwater upwells to the surface water column, heterotrophic bacteria production has no significant positive relationship with phytoplankton biomass, but is positively correlated with freshwater fraction. This suggests that DOC in glacial meltwater, rather than phytoplankton, provides DOC to support enhanced bacteria production. Our results imply that global warming–related increases in glacial meltwater may stimulate heterotrophic bacterial metabolism that respires DOC to CO2, thereby reducing carbon sequestration efficiency in Antarctic coastal waters.
Key Points
Unlike the sea‐ice melting system, enhanced bacterial production (BP) in the eastern Getz Ice Shelf (GtzIS) was uncoupled with phytoplankton biomass
Dissolved organic carbon in glacier meltwater likely stimulates BP on the eastern GtzIS
Warming‐induced glacial melting may weaken carbon sequestration in the Antarctic Ocean by stimulating heterotrophic bacterial metabolism
We present results on phytoplankton and bacterial production and related hydrographic properties collected on nine annual summer cruises along the western Antarctic Peninsula. This region is strongly ...influenced by interannual variations in the duration and extent of sea ice cover, necessitating a decade-scale study. Our study area transitions from a nearshore region influenced by summer runoff from glaciers to an offshore, slope region dominated by the Antarctic Circumpolar Current. The summer bacterial assemblage is the product of seasonal warming and freshening following spring sea ice retreat and the plankton succession occurring in that evolving water mass. Bacterial production rates averaged 20mgCm−2d−1 and were a low (5%) fraction of the primary production (PP). There was significant variation in BP between regions and years, reflecting the variability in sea ice, chlorophyll and PP. Leucine incorporation was significantly correlated (r2 ranging 0.2–0.7, p<0.001) with both chlorophyll and PP across depths, regions and years indicating strong phytoplankton–bacteria coupling. Relationships with temperature were variable, including positive, negative and insignificant relationships (r2<0.2 for regressions with p<0.05). Bacterial production is regulated indirectly by variations in sea ice cover within regions and over years, setting the levels of phytoplankton biomass accumulation and PP rates; these in turn fuel BP, to which PP is coupled via direct release from phytoplankton or other less direct pathways.
► Bacterial and primary production measured at >400 stations on the West Antarctic Peninsula, 2003–11. ► Bacteria and phytoplankton are strongly coupled over depth, regions and years. ► Sea ice duration influences bacterial variability via mixed layer depth and primary production.
Since it is known that hyaluronic acid contributes to soft tissue growth, elasticity, and scar reduction, different strategies of producing HA have been explored in order to satisfy the current ...demand of HA in pharmaceutical products and formulations. The current interest deals with production via bacterial and yeast fermentation and extraction from animal sources; however, the main challenge is the right extraction technique and strategy since the original sources (e.g., fermentation broth) represent a complex system containing a number of components and solutes, which complicates the achievement of high extraction rates and purity. This review sheds light on the main pathways for the production of HA, advantages, and disadvantages, along with the current efforts in extracting and purifying this high-added-value molecule from different sources. Particular emphasis has been placed on specific case studies attempting production and successful recovery. For such works, full details are given together with their relevant outcomes.
Temperate shelf seas are productive areas with the potential to export high quantities of particulate organic carbon (POC), as sinking particles, to the sediments or off‐shelf to the open ocean. The ...amount of carbon which can be exported depends partly on the amount of POC produced and on the remineralization processes occurring on the sinking material. Here, we assessed the relative seasonal importance of microbial respiration and bacterial production associated with suspended, slow‐ and fast‐sinking particle fractions. The three fractions were collected in the Celtic Sea above and below the seasonal thermocline in November 2014, April and July 2015 using Marine Snow Catchers. The slow‐sinking fraction had higher microbial respiration and bacterial production rates than the fast‐sinking fractions, and these two fractions sustained rates of microbial respiration and bacterial production between 1 and 3 orders of magnitude lower than the suspended fraction. This low contribution of the slow‐ and fast‐sinking fractions was consistent with their low contribution to the POC concentration at the two depths sampled. The POC‐specific respiration rates associated with the slow‐ and fast‐sinking fractions were low (median 0.17 and 0.08 d−1, respectively), indicating low‐sinking particle degradation. Our results indicate that ∼5% of the POC in surface waters can be exported below the thermocline.
Key Points
Higher microbial respiration and bacterial production rates estimated in slow‐sinking compared to fast‐sinking fractions in shelf waters
Due to the low number of particles in the fast‐sinking fraction, their contribution to water column metabolism was low
Slow‐sinking fraction made the greatest contribution to the potential export of particulate organic carbon to sediments or off‐shelf
We investigated bacterial production (BP) and respiration (BR), as well as the physico-chemical properties of the water column, to elucidate the effect of upwelling on heterotrophic bacterial ...metabolic activities and growth efficiency (BGE) in July 2012 and May 2013 in the Ulleung Basin (UB), East/Japan Sea. The upwelled conditions were characterized by higher chlorophyll-a (Chl-a) concentrations resulting from the upward shift of the nitracline compared to that of the non-upwelled condition. Analyses of the size fractions of Chl-a and pigment composition revealed that large size phytoplankton (> 20µm), mainly consisting of diatoms, appeared to be the major phytoplankton component. BP and BR were significantly correlated with Chl-a (P < 0.001), but the correlations with temperature were not significant (P > 0.05). These results suggest that bacterial metabolic activities are stimulated by the availability of organic resources enhanced by upwelling in the UB. Further statistical analysis showed that the difference in BP and BGE with variations in upwelling intensity were significant (P = 0.018 for BP, P = 0.035 for BGE), but the difference in BR was not significant (P = 0.321). These results suggest that metabolic energy is partitioned more for BP under a strong upwelling condition, i.e. high nutrient and Chl-a conditions. In contrast, the energy generated via respiration was partitioned more for maintaining metabolism rather than for biomass production under weakly or non-upwelled conditions, i.e. stratified and low Chl-a conditions. Overall, our results suggest that any changes in upwelling intensity would significantly affect the carbon cycle associated with the fate of primary production, and the role of the microbial loop in the UB where changes in the intensity and frequency of upwelling associated with climatic changes are in progress.
To understand mechanisms linking ecosystem processes and microbial diversity in freshwater ecosystems, bacterial productivity and the metacommunity dynamics of species sorting and mass effects were ...investigated in an 18 ha headwater lake in northern Alaska. On most sampling dates, the phylogenetic composition of bacterial communities in inflowing streams (inlets) was strikingly different than that in the lake and the outflowing stream (outlet) (16S DGGE fingerprinting), demonstrating the shift in composition that occurs as these communities transit the lake. Outlet and downstream communities were also more productive than inlet and upstream communities ((14)C-leucine incorporation). Inlet bacteria transplanted to the outlet stream in dialysis bags were equally or less productive than control bacteria, suggesting that the inlet bacteria are capable of growing under lake conditions, but do not remain abundant because of species sorting in the lake. Outlet bacteria (representative of epilimnetic bacteria) transplanted to the inlet stream were less productive than control bacteria, suggesting that lake bacteria are not as well adapted to growing under inlet conditions. Based on water density, inlet stream water and bacteria generally entered the lake at the base of the epilimnion. However, during low to medium flow in the inlet stream the residence time of the epilimnion was too long relative to bacterial doubling times for these allochthonous bacteria to have a mass effect on the composition of outlet bacteria. The highest community similarity between inlet and outlet bacteria was detected after a large rain event in 2003, with over 61% similarity (average non-storm similarities were 39 ± 8%). While mass effects may be important during large storm events, species sorting appears to be the predominant mechanism structuring bacterial communities within the lake, leading to the assembly of a lake community that has lost some ability to function in stream habitats.
Polar waters may be highly impacted by ocean acidification (OA) due to increased solubility of CO2 at colder water temperatures. Three experiments examining the influence of OA on primary and ...bacterial production were conducted during austral summer at Davis Station, East Antarctica (68°35′ S, 77°58′ E). For each experiment, six minicosm tanks (650L) were filled with 200μm filtered coastal seawater containing natural communities of Antarctic marine microbes. Assemblages were incubated for 10 to 12days at CO2 concentrations ranging from pre-industrial to post-2300. Primary and bacterial production rates were determined using NaH14CO3 and 14C-leucine, respectively. Net community production (NCP) was also determined using dissolved oxygen. In all experiments, maximum photosynthetic rates (Pmax, mgCmgchl a−1h−1) decreased with elevated CO2, clearly reducing rates of total gross primary production (mgCL−1h−1). Rates of cell-specific bacterial productivity (μgCcell−1h−1) also decreased under elevated CO2, yet total bacterial production (μgCL−1h−1) and cell abundances increased with CO2 over Days 0–4. Initial increases in bacterial production and abundance were associated with fewer heterotrophic nanoflagellates and therefore less grazing pressure. The main changes in primary and bacterial productivity generally occurred at CO2 concentrations >2× present day (>780ppm), with the same responses occurring regardless of seasonally changing environmental conditions and microbial assemblages. However, NCP varied both within and among experiments, largely due to changing nitrate+nitrite (NOx) availability. At NOx concentrations <1.5μM photosynthesis to respiration ratios showed that populations switched from net autotrophy to heterotrophy and CO2 responses were suppressed. Overall, OA may reduce production in Antarctic coastal waters, thereby reducing food availability to higher trophic levels and reducing draw-down of atmospheric CO2, thus forming a positive feedback to climate change. NOX limitation may suppress this OA response but cause a similar decline.
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•Elevated CO2 decreased primary productivity and gross primary production.•Elevated CO2 decreased bacterial productivity but increased bacterial production.•Increased bacterial production was associated with reduced grazing pressure.•Elevated CO2 decreased net community production when nitrate was available.•Under nitrate limitation net community production responses to CO2 were suppressed.
The importance of terrestrial-derived organic matter for lake zooplankton communities remains debated, partly because little is known about the basic pathways by which allochthonous carbon is ...transferred to zooplankton, and whether these vary among the major taxonomic and functional groups. We quantified allochthony of three zooplankton groups (
Cladocera
,
Calanoida
, and
Cyclopoida
) across 18 lakes in Québec, spanning broad gradients of dissolved organic matter (DOM) and lake trophy, using a multi-isotope (δ
2
H + δ
13
C), multi-source (terrestrial, phytoplanktonic, benthic) approach. All three zooplankton groups had significant levels of allochthony, but differed greatly in their respective patterns across lakes. Allochthony in
Calanoida
and
Cyclopoida
was linked to detrital food chains based on particulate organic matter (POM) and on DOM, respectively, whereas in
Cladocera
it appeared related to both pathways; not surprisingly this latter group had the highest mean allochthony (0.31; compared to 0.18 in
Cyclopoida
and 0.16 in
Calanoida
). This study highlights the complexity of the pathways of delivery and transfer of terrestrial organic matter in freshwaters, and underscores the role that microbial food webs play in this transfer.
We investigated changes in heterotrophic bacterial metabolic activities and associated carbon cycles in response to a change in dominant phytoplankton communities during two contrasting environmental ...conditions in austral summer in the Amundsen Sea polynya (ASP), Antarctica: the closed polynya condition in 2014 (ANA04) and the open polynya condition in 2016 (ANA06). In ANA04,
Phaeocystis antarctica
predominated phytoplankton biomass, comprising 78% of total phytoplankton carbon biomass, whereas diatoms and
Dictyocha speculum
accounted for 45% and 48% of total phytoplankton carbon biomass, respectively, in ANA06. Bacterial production (BP) showed a significant positive correlation with only chlorophyll-a (Chl-a, rho = 0.66,
p
< 0.001) in
P. antarctica
-dominated ANA04, whereas there were significant positive relationships of BP with various organic carbon pools, such as chromophoric dissolved organic matter (CDOM, rho = 0.84,
p
< 0.001), Chl-a (rho = 0.59,
p
< 0.001), and dissolved organic carbon (DOC, rho = 0.51,
p
= 0.001), in ANA06 when diatoms and
D. speculum
co-dominated. These results indicate that BP depended more on DOC directly released from
P. antarctica
in ANA04, but was supported by DOC derived from various food web processes in the diatom-dominated system in ANA06. The BP to primary production (BP : PP) ratio was three-fold higher in
P. antarctica
-dominated ANA04 (BP: PP = 0.09), than in diatom- and
D. speculum
-co-dominated ANA06 (BP : PP = 0.03). These results suggested that the microbial loop is more significant in
Phaeocystis
-dominated conditions than in diatom-dominated conditions. In addition, the decreases in BP : PP ratio and bacterial respiration with increasing diatom proportion in the surface mixed layer indicated that the change from
P. antarctica
to diatom predominance enhanced biological carbon pump function by increasing particulate organic carbon export efficiency. Consequently, our results suggest that bacterial metabolic response to shifts in phytoplankton communities could ultimately affect larger-scale ecological and biogeochemical processes in the water column of the ASP.
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